1. Field of the Invention
The invention pertains to jet-powered personal watercraft, and more particularly, to an intake grating with a foil that directs the flow of intake water so as to provide increased stability, speed and improved handling of the craft.
2. Description of Prior Art
Jet powered personal watercraft (hereafter "craft") have become enormously popular in recent years. In a predominant configuration the craft is powered by a small engine located toward the front of the craft's hull. An intake channel is formed in the bottom of the hull somewhat aft of the engine. The channel extends aft to abut a jet pump housing. An impeller is located in the housing positioned coaxially with the engine and connected to it by a drive shaft which extends through the wall of the intake channel. Additionally, a stator is typically fixed in the jet pump housing just aft of the impeller. In operation, the forward motion of the craft, along with the power applied to the impeller, draws in water through the intake channel and propels it out the rear of the pump to produce forward thrust. Steering may be accomplished by providing a mechanism to laterally divert the water as it exits the jet pump.
One disadvantage of the typical craft design is that at high speeds the intake water flow is not uniform across the area of the impeller. Less water is directed toward the upper portion of the impeller relative to the lower portion resulting in diminished efficiency. Rhoda, U.S. Pat. No. 3,757,728 discloses a fixed guide vane which functions as a scoop to provide water flow toward the top of the impeller in a large jet-powered boat. This structure protrudes below the plane of the hull to force all the intake water through the upper section of the channel when the boat is operating at maximum speed. Such a scoop has a number of disadvantages when used with smaller, personal watercraft. Personal watercraft make relatively sharp turns and are thus subject to high yaw angles. At a high yaw angle the opening of Rhoda's scoop would not be aligned with the flow of water, thus actually resulting in decreased water flow and craft speed. At the high speeds involved with personal watercraft, the Rhoda scoop would also produce undesirable drag forces and pitching moments, reducing stability. Moreover, contrary to the Rhoda design it is more desirable to have a relatively flush bottom from the standpoint of safety to protect both swimmers and riders. Moreover, as personal watercraft have much smaller engine capacity and pump cavities, the design must be more efficient for satisfactory control and operation.
To avoid damaging the drive train, it is desirable to place some form of grating across the opening in the hull so as to prevent the entrance of large objects into the intake channel. Such a grating is seen in Richardson U.S. Pat. No. 4,237,812. Richardson discloses a grating with a slight scoop formed in the rear of the opening. It does not provide the improvement in stability maneuverability and acceleration of a foiled design.
Moyle, U.S. Pat. No. 5,114,368, attempts to solve this problem by bringing the vane, referred to as a top loading plate, within the intake channel. The vane is supported by a single vertical shaft shielding partition. However, this design suffers from three principal disadvantages. First, use of a single partition does not adequately achieve the grating function. Second, the attachment of the vane to the single partition is structurally unsound because it is not able to adequately resist torque on the vane and, is thus subject to fatigue. Third, the partition may interfere with water flow when the craft is at yaw angles.